Protection of multiphase transmission lines



Oct. 13,1942.

H.. THOMMEN 2,298,517

PROTECTION OF MULTIPHASE TRANSMISSION LINES Filed Feb. e, 1940 /c` \`0 /bw Vj Vl] 7c /3 r (v C /50 /w f 4C Patented oet. 13, 1942 PROTECTION 0F MULTIPHASE TRANSMIS- SION LINES Hans Thommen, Baden, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie., Baden, Switzerland Application February '6, 1940, serial No. 317,605

- phases.

In Germany November 17, 1938 3 Claims.

This invention relates to the protection of multi-phase transmission lines comprising three or more phases from damage arising from arcing short circuits to ground.

A method for the protection of multi-phase transmission lines having quick-acting reclosing circuit breakers in each phase is already known. In view of the much greater number ofsingle phase disturbances in multi-phase transmission" networks as compared with disturbances which affect all the phases simultaneously, it has already been proposed to individually control the circuit breakers in each phase by means of relays lin such a way that in any disturbance only the circuit breaker of the phase or phases on which a fault occurs is actuated. In this method a synchronizing force is maintained in the phases which are not disturbed so that the danger of the network falling out of phase is minimized.

It has been found that a longer time is required for de-ionization of the arc ln the case of single phase short circuits than in the case of disturbances in a plurality of phases.

The present invention is an improvement in the protection of multi-phase circuits against disturbances by arcing shorts which comprises increasing the period between opening and reclosing the line in the case of disturbances in a single lthe control mechanism of one phase and the l control mechanism that is common to a plurality phase as compared with the period between opening and reclosing in the case of simultaneous disturbances on more than one or on all of the phases.

' The invention may be carried out by including in the regulating mechanism for the circuit breakers an auxiliary time delay device in such a manner that the auxiliary time delay device comes into action only when the circuit breaker of only a single phase is actuated and is unefective when a disturbance occurs in a plurality of In this manner, the inclusion of the additional time delay in the reclosing mechanism depends upon the character of the disturbance and the period for de-ionization of the arc is adapted to the nature of the circuit breaking operation. p

The time delay device may comprise any known device such as clockwork, mechanical or electrical damping device, or the like. The operation of the circuit breaker mechanisms can be effected in known manner pneumatically, electrically, electro-pneumatically or by remote control.

In the accompanying drawing which illustrates one embodiment of the invention:

Fig. l is a schematic view of a multiphase protective system in which the timing mechanism of phases.

In Fig. l nthe reference characters A, B, and C indicate the feeders of a three phase system to which the branch lines a, b, c, respectively, are connected. The control mechanism for each feeder line is of identical design and the reference numerals for the corresponding elements of the several .phases are distinguished from each other by letters indicative of the respective phases. For simplicity of description, only the control apparatus of branch line a will be described in detail. it being understood that similar equipment is associated with branch lines b and c.

The usual over-current relay la is included in branch a, to complete a series circuit from a local direct current source B through the winding of arelay 2a and the winding 3a of an electrically operated valve la of an electro-pneumatic relay 5a when the current flow in branch line a. exceeds some predetermined value.

The relay 5a controls the supply oi' air under pressure from a storage tank 6 to the operating cylinder 'la of an air-blast circuit breaker 8a in the branch line a. As shown in Fig. 2, the relay 5a comprises a valve 9 that is carried by a piston I0 and normally retained in closed position by a spring Il to block pressure ow from the reservoir 6 to the conduit I2a. The pilot or control valve |3a is opened, upon current flow through the winding 3a, to admit pressure air to the rear of the piston HJ, and the resulting movement of the latter opens the valve 9 to admit pressure air to the c'onduit |2a. The conduit I2a opens into the operating cylinder 1a of the circuit breaker and, through an adjustable throttling valve lla, into the chamber lia of time delay mechanism that determines the reclosing of the circuit breaker 8a. A pipe I 6a connects the rear end of chamber I5a to the relay 5a at a point in advance of the piston I0, but air ow through this pipe is normally blocked by a spring pressed valve ila. The valve Ila opens when the pressure builds up in the forward end of chamber I5a, and thus establishes the same pressure at opposite sides of the piston I0, thereby permitting the spring il to close the valve 9 that admits pressure air to the conduit I2a. The pilot valve |3a had already closed as the relay circuit through the winding 3a was opened at the relay la when the circuit breaker 8a opened. The interruption of the supply of pressure air to the operating cylinder la results in the reclosure ofn the circuit breaker 8a by spring or pneumatic means,

' not shown, as the pressure fluid within the cylmore rapid reclosing when a plurality of the circuit breakers open in response to a fault on more than one phase. The Vnormally open contacts of the relays 2a, 2b, 2c of the' control circuits of the several phases are included, in series, in a circuit from't'he current source B' to the operating winding I8 of the valve I9 in the pres- In accordance with this invention, addi-` tional control mechanism is provided to obtain a4 sure supply line to cylinder 20. 'Ihe piston 2| is connected to a. crank arm on the rock shaft 22 which has crank arms 23a- 23o for Voperating the slide rods 24a-24 of the respective relays 5a, 5b, 5c. As shown in Fig. 2, the rod 24al carries a slide valve 25a that normally closes the passage 26a which opens into the operating cylinder at y opposite sides of the piston I0. Valve 25a is shifted to the right `upon a counterclockwise movement of rockshaft 22 when pressure air is admitted to the cylinder 20 below the piston 2|, and the same action takes place'in the relays 5b and 5c. The time delay mechanisms of the several circuit breakers are thus rendered ineective as the pressuresat the opposite'faces-of the pistons I0 are equalized by the opening of the slide valves, and the springs then force thepistonsA l0 into normal position to close the main valves 8.

A fault-on any one phase will energize the overload relay of that phase, for example the relay la of the line a., The associated relay 2a'is closed and current is supplied to the winding 3a to open the pilot valve |3a rof relay 5a. The main valve 9 then opens and pressure air ows through conduit |2a to the operating cylinder '|a of the circuit breaker 8a, and to chamber |5a of the time delay mechanism. TheA circuit breaker 8a opens to interrupt current owon line a, and recloses again Ywhen the pressure in chamber |50, builds up to that value which will open the valve lla. In the case of a fault that affects all of the branch lines, Ythe control ,circuits of all phases are energized and all of the 'circuit breakers are opened. The simultaneous energization of the relays 2a, 2b, 2c completes the circuit of the valve-operating winding I8, and pressure air flows into cylinder 20 to lift the piston 2| and thereby shift thev slide valves toopen position. The resultant equalization of the pressures acting on the several pistons I0 permits the reclosure of the main valves 9 by springs Il, and the several circuit breakers then reclose without awaiting the expiration of the time delay interval.

The illustrated circuit for the valve-operating winding |8 requires the energization of the three relays 2a, 2b and 2c, but it will be apparent that these relays may be provided with a plurality of sets of contacts for completing alternative circuits for the winding |8 upon the simultaneous energization of any two of the relays.

Itis to be understood that the invention is not restricted to the electro-pneumatic type of control system as other systems have been or may be used with the individual phases. The

invention contemplates the addition to a pro-V tective system in which reclosing circuit breakers are individually controlled by a lfault condition on the `associated phase, of a further control for obtaining a more rapid reclosure when a plurality of the circuit breakers are opened simultaneously.

I claim:

1. A protective system for a multiphase transmission line comprising a reclosing circuit breaker for each phase, relay mechanism individual to the several phases for selectively opening the cir- .cu.it breaker of a phase on which a fault occurs, timing mechanism individual to each Y circuit breaker for delaying the reclosure thereof, and

means responsive to the simultaneous energize.-

tion of a plurality of said relay mechanisms to render said timing mechanisms linoperative, thereby to provide a longer period of deionization when a single phase is opened than when a plurality of phases are opened.

2. In a system for the protection of a multiphase transmission line, a reclosing circuit breakler for each phase,- means individual to each circuit breaker for opening the same, timingmea-ns individual to each circuit breaker for delaying the reclosure thereof, an overload relay on each phase, a relay circuit controlled by each overload relay, each relay circuit including an auxiliary relay and means for energizing the opening means of theA circuit breaker of the associated phase, an additional relay circuit energized by the simultaneous energization of -a plurality of said auxiliary relays, and meansjcontrolled by said additional relay circuit for rendering inoperative the timing means of the `several circuit breakers.

3. In a system for the protection of a multiphase`I transmission line, the combination with a 'reclosing circuitl breaker for each Vphase, and means individual to each circuit breaker for opening and for reclosing the same, said means including for each ycircuit breaker timing means to delay the reclosure of the circuit breaker for apreselected interval, of means responsive to simultaneous faults on a plurality of phases for l rendering said timing mechanisms inoperative to delay the reclosures of the associated circuit breakers.

HANS 'I'HOli/IMEN. 

